ON MADDER. 
127 
them have the fault of being too exact, or too difficult and 
too long of execution. I will now point out those which I 
think preferable, and which I have long since employed in 
the examination of madders which I continually make. 
One of these means consists in determining the coloring 
power by means of Labillardiere's colorimeter ; the second, 
in determining this coloring power, as well as the solidity 
and brilliancy of the colors, by an operation of dyeing. The 
third experiment is to ascertain the absolute quantity of the 
coloring principle. 
These different experiments are always made compara- 
tively, by taking for type a madder prepared with all possi- 
ble care, and having the same marks as that under exami- 
nation. As with indigo and other tinctorial substances, a 
single experiment is not sufficient ; and by reason of the 
difficulty there is of correctly verifying the value or the 
quality of the madders, it is indispensable, in order to decide 
with any certainty, to check the experiments by each other. 
This is the only way of obtaining satisfactory results. 
1. Determination of the coloring Power by the Colori- 
meter. — The following is the mode of operation with the 
colorimeter of Labillardiere. The type madder and the 
madder under examination are dried at 262° Fahr., and an 
account is kept of the respective quantities of hygrometric 
water they contain. 
25 grms. of each sample are then mixed with 250 grins, 
of water at 6S°. After three hours of contact, the whole 
is thrown upon a linen cloth. A second maceration is made 
with the same amount of water and for the same length of 
time. The madders are then washed with 250 grms. of 
cold water, dried at 2 12°, and weighed, in order to ascertain 
the proportions of soluble, saccharine and mucilaginous mat- 
ters which they have lost by these preliminary washings, 
which only remove an insignificant quantity of red color- 
ing matter. 
5 grms. of each of the two madders are then introduced 
